ASUS PRIME B350-PLUS: SATA SSD does not show in BIOS when M.2 SSD is installed

[Adrian_50]

This is the situation:
I have installed
1863GB Western Digital WDC WD20EFRX-68EUZN0 (SATA)
232GB Samsung SSD 850 EVO 250GB (SSD)
on my desktop. This works perfectly fine, where I have Windows 10 installed on the Samsung SSD.

I then tried to move an M.2 Kingston SSD from my broken laptop to my desktop. See this image for model:
https://photos.app.goo.gl/OjWboqtQJnGCDfhO2
This was of course installed directly on the M.2 socket on my ASUS PRIME B350-PLUS motherboard. This SSD has the old operating system, which I am not interested in using, but I want to backup other files on this SSD. Then I can format.

Now the problem:
When I boot, I am only able to boot the old operating system on the M.2 SSD, and not to OS on the Samsung SSD. I seem to be able to use the old operating system, although the drivers are completely wrong, of course.
In BIOS I can only see the M.2 SSD and the HDD, not the Samsung SSD. I have tried different boot orders, which did not make any difference.

When I removed the M.2 Kingston SSD, I was able to boot like normal, and now everything seems to be like before I installed the M.2 SSD.

I have BIOS version 0808.

I have only one suggestion, but I am not sure if it matters:
The HDD is connected to SATA_1 on the MOBO, while the Samsung SSD is connected to SATA_6. Should I try to move the SSD to SATA_2?

 

[kraelic]

Reading the manual it says the sata 5/6 ports are disabled when using the m.2 slots. You can use 1 2 3 or 4 for hard drives and 2.5 ssd and then 5 and 6 go to m.2 in sata mode

Populating the m.2 disables the sata 5 and 6 on the board. Sata or PCIe

 

[Adrian_50]

Reading the manual it says the sata 5/6 ports are disabled when using the m.2 slots. You can use 1 2 3 or 4 for hard drives and 2.5 ssd and then 5 and 6 go to m.2 in sata mode

Populating the m.2 disables the sata 5 and 6 on the board. Sata or PCIe

Nice find. I tried moving the Samsung SSD to Sata_2, and now it works. Thanks!